In the step of forming the S/D region in a 3D-structured MOSFET, representative examples of which are a fin-FET and a tri-gate MOSFET, it has become increasingly difficult to ensure the controllability of. the profile of impurities ion-injected and to re-crystallize the thin-film fin rendered amorphous.
To solve this problem, a metal S/D-MOSFET has been proposed, which can be manufactured, without the necessity of injecting ions in such a high dose as would render the thin-film fin amorphous (see, for example, Jpn. Pat. Appln. KOKAI Publication No. 2006-100600). In this metal S/D-MOSFET, the S/D region and the extension region consist of silicide (e.g., NiSi or Ni(Pt)Si). However, the overlap length for which the extension region overlaps the gate has not been positively controlled, though the overlap length is important because it determines the current-drive and immunity tohort-channel-effect of the MOSFET.
Further, it is difficult to control the diffusion of Ni in the S/D region, because of the amount of nickel (Ni) deposited, the temperature changes during the reaction, and the like. Particularly in any region where the fin width is 30 nm or less, it is very hard to control the thickness of the silicide film. Because of this problem, the fin body may be completely changed to silicide. If the fin body is completely changed to silicide, the current path extending from the channel to the drain region consisting of silicide is restricted. It causes inevitably increasing parasitic resistance and greatly degrading the current-drive. Moreover, in any system using SOI, abnormal growth or condensation locally occurs because of the thermal gradient resulting from the low thermal conductivity of the BOX layer. This makes it extremely difficult to control the thickness of the silicide film and the overlap length.